Patent Document 1 discloses a magnetic wave gear device in which a high-speed rotor, a low-speed rotor, and a stator are rotatable relative to one another around a rotation axis. In a case where the magnetic wave gear device is used as, for example, an electric motor, the stator is provided with coils. Harmonic magnetic flux is generated by rotating the high-speed rotor by magnetomotive force of the coils, and the low-speed rotor serving as an output shaft rotates at a predetermined speed reduction ratio (speed reduction ratio of the low-speed rotor to the high-speed rotor) by using the harmonic magnetic flux. In this case, the magnetic wave gear device has two functions of a magnetic speed reducer and of a brushless motor.
In principle, the magnetic wave gear device can obtain a predetermined speed reduction ratio (or a speed increasing ratio) in a state where a rotor and a stator do not contact each other, and therefore has characteristics of low friction, low noise, and excellent durability compared to a mechanical speed reducer (or a mechanical speed increaser). In addition, as described above, since the magnetic wave gear device has functions of a speed reducer and of an electric power generator (electric motor) if the stator is provided with coils, it is possible to adopt a configuration of what is called direct drive in which a speed reduction mechanism is omitted and an electric power generator and a rotary shaft are directly connected to each other. Accordingly, the magnetic wave gear device has been tried to be used as, for example, a direct drive-type power generator main body of a wind power generator in which the power generator main body is disposed at a height of several tens of meters from the ground and a lot of effort is required for maintenance of a speed increaser (refer to Patent Document 2).
The magnetic wave gear device includes a type (hereinafter, may be referred to as a “double-sided magnet type”) which has been researched and developed by the United Kingdom University of Sheffield and another type (hereinafter, may be referred to as a “single-sided magnet type”) which has been researched and developed by Osaka University (to which part of the inventors of this application belongs) (refer to FIGS. 10 and 11 of Patent Document 2). Briefly describing the difference in configuration of the two types, the double-sided magnet type is a type including permanent magnets provided in the high-speed rotor and in the stator, and the single-sided magnet type is a type including permanent magnets provided only in the high-speed rotor.